Cancer can be viewed as a state in which the balance between cell proliferation and cell death aberrantly favors the former. We and others have discovered that the intracellular redox environment exerts a profound influence on the normal cellular processes that regulate the balance between proliferation and cell death, including DNA synthesis, enzyme activation, cell cycle progression, proliferation, differentiation, and apoptosis. In fact, it could be argued that redox homeostasis is central to the governance of cell fate. Unfortunately, molecular mechanisms mediating redox sensitivity and regulation within cells are still poorly defined. Current pharmacological methods to alter intracellular redox state are limited by (i) their inability to operate independent of global biochemical alterations and cellular toxicity, and (ii) the required significant manipulation of culture conditions that perturb intracellular homeostasis. Our genetic constructs overcome these limitations as they enable real-time and extended assessment of alterations in intracellular redox without cellular disruption. These constructs use fluorescence resonance energy transfer (FRET), a distance- and orientation- dependent energy transfer process between donor and acceptor fluorophores. In these biosensors a change in redox induces a conformational change in the redox-sensitive switch that links the donor and acceptor, changing their distance, which in turn causes a detectable change in FRET efficiency. Here we propose to further define the sensitivity and dynamic range of our FRET biosensors relative to changes in the intracellular redox environment that appear to dictate cell fate. Advantages of this approach include: (1) the ability to quantify the change in redox state;(2) independence of sensor concentration;and (3) the ability to precisely tune the redox sensitivity and range by exchange of the switch or the fluorophore modules in the construct. Aim 1: Define the sensitivity and dynamic range of genetically engineered FRET redox biosensors during proliferation by comparison of nontransformed fibroblasts and isogenic porcine tumor cell lines with respect to the presence or absence of contact inhibition. Specifically, detection of physiologically relevant changes during successive stages of cell growth is proposed. Aim 2: Determine the extent to which the FRET biosensors are sensitive to changes in the intracellular redox environment of isogenic HCT116 p53+/+ and p53-/- cells treated with the chemotherapeutic drugs fluorouracil and doxorubicin in combination with perturbations in glutathione homeostasis. Specifically, the intracellular redox environment will be visualized in response to common chemotherapeutic drugs in combination with agents that modulate biosynthesis or metabolism of glutathione. Aim 3: Create second generation FRET biosensors that permit visual monitoring and dissection of intraorganellar local redox potentials. Specifically, we intend to quantify differences in redox potentials within subcellular organelles that are at a nonequilibrium steady-state with respect to each other in living cells. In sum, the proposed work will provide novel molecular tools that enable in depth examination of the role of redox signaling at the intracellular and intraorganellar level in cancer development. PUBLIC HEALTH RELEVANCE: This project pursues novel molecular tools-redox-sensitive biosensors-that will enable in depth examination of the role of redox signaling in cellular processes related to cancer development. Optimization of these biosensors will enable visualization of local changes in redox potential that might regulate progression through the cell cycle and mediate contact-dependent inhibition of cell growth, the disruption of which is a key hallmark of cancer. Ultimately, the tools will enhance understanding of the extent to which cancerous cells have lost the ability to mount changes in redox potential that accompany normal cell growth versus their sensitivity to these changes.